1. Field of Invention
The invention relates to a circuit arrangement for selective generation of an analog current output value or an analog voltage output value as a function of an analog input value. Optionally, an input base value and/or a signed input correction value may also serve as inputs as well. The invention employs a current control unit, a voltage control unit, a current output source that is triggered by the current control unit, and a voltage output source that is triggered by the voltage control unit.
2. Description of Related Art
In the prior art, measuring devices are known that detect a physical quantity as a measured value. For example, temperature, pressure, flow rate, liquid level, or an electrical quantity, such as current, voltage or wattage, are detected and made available in the form of an analog measured value. The prior art has also known standardization of the measured values that are made available by the measuring devices of the aforementioned types, so that instead of the analog measured values which are made available or detected first, measured values that have been standardized for further processing in control circuits are available. Current values from 4 to 20 mA have been used as standardized measured values, as well as current values from 0 to 20 mA. Similarly, voltage values from 0 to 10 V have been extensively introduced in industrial practice as standardized measured values.
In conventional circuit arrangements for generating these types of output values, the current control unit and the voltage control unit are often made as operational amplifiers, while the current output source and the voltage output source generally include a transistor. Typically, the current output source operates with a Darlington transistor stage or with several Darlington transistor stages to keep the triggering base currents as low as possible.
Conventional circuit arrangements of this type have employed either a triggered current output source or a triggered voltage output source. The selective triggering of the current output source or the voltage output source has been previously accomplished using complex circuitry. In particular, past attempts included circuits requiring more than two operational amplifiers, with some circuits employing as many as four or five operational amplifiers to perform the selective triggering.
Consequently, what is needed is a circuit arrangement capable of providing standardized measured values and perform the selective triggering that can be built more easily and more economically than known circuit arrangements.